Nowadays, a screw fastening device comprises a bolt connection, bolt-nut connection and a double-end bolt-nut connection. These loosening-proof methods and devices include:
(1) Friction Loosening-Proof
This method usually includes double nuts and an elastic gasket. The double nuts provide additional pressure and friction to the screw threads. However, it is limited to the stable, low speed and heavy-loaded screw fastening devices while not violent impact or vibrancy. The elastic gasket loosening-proof means provide a counter force. The pressed elastic gasket makes the screw threads (of both the bolts and nuts) press intensively and the inclined tips of the gaskets are set in opposition to the nuts as well as the contacting face of the fastened object, so that the loosening-proof could be realized. Such a method or device also has its own shortage so that the angle of rotation for loosening-proof lies in 3-4° and is not suitable for fastening units with violent impact or vibrancy.
(2) Mechanical Loosening-Proof
This method usually includes a cotter dowel and a grooved hexagonal nut. The method is realized by inserting the cotter dowel into the small hole of the common bolt or double-end bolt and the groove of the nut. The rear part of the cotter dowel is pulled apart and alongside the nut. The shortages of this method and device are the limitation to its use circumstances, for example it can not be used for countersinking and is inconvenient to install or uninstall.
(3) Material Loosening-Proof
This method usually includes applying liquid adherent between the screw threads. The shortage of this method is that it is inconvenient to uninstall and it can not be reused or can be reused for limited times.
(4) Riveting Loosening-Proof
A rivet is inconvenient to uninstall and can not be reused, so it is limited to its usage.